Origins of Human Heart Beat Traced Back One Billion Years

Luke Walker

“You are the product of 3.5 billion years of evolutionary success. Act like it.” 

While we all fundamentally know that all of life on Earth is interconnected, it isn’t always easy to see how those connections have played out over time. After all, what do human beings really have in common with a jellyfish? Well, according to a new study led by Penn State’s Tim Jegla, the cellular processes that cause our heart to beat is shared with cnidarians and likely originated about 700 million to one billion years ago. The results of the study have been published in the Proceedings of the National Academy of Sciences

Cells of heart muscle contract automatically. Even when grown from stem cells in a petri dish, the cells will beat on their own. The cells don’t all constrict at once, but in a wave in order to pump blood through the heart. If everything happened at once, the muscle would just seize up and not function at all. Cnidarians utilize similar coordinated movements to move around in their environment, as they don’t have a central brain that allows them to sense, analyze, and respond to factors around them; the neuronal activity is spread throughout the organism.

Jegla’s lab studied Nematostella vectensis, commonly known as the starlet sea anemone, to explore these similarities. They found that humans and N. vectensis share an analogous gene family known as Erg which times the movements through an ion channel. This genetic information has changed since our last common ancestor with cnidarians about one billion years ago.

“This discovery,” Jegla said in a press release, “shows that at least some of the molecular mechanisms through which we control electrical activity in things like the heart evolved in some of the earliest animals, long before the existence of hearts or even cardiac tissue.”

“We make the case in this paper,” he goes on, “that the properties of the human Erg channel and the ancient Nematostella channel are tuned extremely well to repolarize the long action potentials that you need to get a strong muscular contraction, or a prolonged wave contraction like you have in a heartbeat. What we'd like to do now is to see if this kind of channel is fundamentally required to get that kind of wave contraction in all animals, and, if so, is that what it initially evolved for? If the slow wave contractions of the body wall are the functional orthologues of heart contraction, then have we adapted that whole preexisting program for the heart? All the other ion channels we use to regulate heart contraction are there, too, in Nematostella. So when we look at what this channel is doing in the human heart and what we can hypothesize it might be doing in the sea anemone, we can begin to see that maybe this is, in fact, what it evolved for.”

Though our brains and fine muscle control might be unparalleled to nearly every animal on the planet, the most fundamental cellular mechanisms that allow those processes to happen is fairly highly conserved throughout most of animal life. Though that might seem self-evident on a basic level, it does give insight into the function of the primitive life that was the last common ancestor between the two groups and provides clues in how animals changed over time.

The lab is now moving beyond the most basic cellular processes and trying to determine how brains originated. They are not only looking for when dendrites and axons evolved, but how and also why, though asking “why” with questions regarding evolution doesn’t always produce clear answers. The team will continue to focus on the sea anemone, as their neurological system is among the most simple on the planet. They hope that understanding the origin of neuroanatomy will eventually reveal answers about the fundamental biological basis of behavior.

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